<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>120</ContextCount>
  <ElementCount>269</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>29</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>5</UnitCount>
  <MyReports>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Condensed Consolidated Statements of Financial Position (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfFinancialPositionUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Financial Position (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - Condensed Consolidated Statements of Financial Position (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfFinancialPositionUnauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Financial Position (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - Condensed Consolidated Statements of Operations (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfOperationsUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Operations (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - Condensed Consolidated Statements of Comprehensive Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfComprehensiveIncomeUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - Condensed Consolidated Statements of Stockholders' Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfStockholdersEquityUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Stockholders' Equity (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004501 - Statement - Condensed Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfStockholdersEquityUnauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1005000 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - New Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/NewAccountingPronouncements</Role>
      <ShortName>New Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Revenue Recognition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/RevenueRecognition</Role>
      <ShortName>Revenue Recognition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Other Current Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/OtherCurrentAssets</Role>
      <ShortName>Other Current Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2111100 - Disclosure - Goodwill</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/Goodwill</Role>
      <ShortName>Goodwill</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Property and Equipment, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/PropertyAndEquipmentNet</Role>
      <ShortName>Property and Equipment, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Accrued Payroll and Benefit Costs</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/AccruedPayrollAndBenefitCosts</Role>
      <ShortName>Accrued Payroll and Benefit Costs</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2120100 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2121100 - Disclosure - Net Income Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/NetIncomePerShare</Role>
      <ShortName>Net Income Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2122100 - Disclosure - Business Segments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/BusinessSegments</Role>
      <ShortName>Business Segments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2123100 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2201201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://roberthalf.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2301302 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Revenue Recognition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/RevenueRecognitionTables</Role>
      <ShortName>Revenue Recognition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/RevenueRecognition</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Other Current Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/OtherCurrentAssetsTables</Role>
      <ShortName>Other Current Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/OtherCurrentAssets</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2311301 - Disclosure - Goodwill (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/GoodwillTables</Role>
      <ShortName>Goodwill (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/Goodwill</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2312301 - Disclosure - Property and Equipment, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/PropertyAndEquipmentNetTables</Role>
      <ShortName>Property and Equipment, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/PropertyAndEquipmentNet</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/Leases</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Accrued Payroll and Benefit Costs (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/AccruedPayrollAndBenefitCostsTables</Role>
      <ShortName>Accrued Payroll and Benefit Costs (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/AccruedPayrollAndBenefitCosts</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2320301 - Disclosure - Stockholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/StockholdersEquityTables</Role>
      <ShortName>Stockholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/StockholdersEquity</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2321301 - Disclosure - Net Income Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/NetIncomePerShareTables</Role>
      <ShortName>Net Income Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/NetIncomePerShare</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2322301 - Disclosure - Business Segments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/BusinessSegmentsTables</Role>
      <ShortName>Business Segments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/BusinessSegments</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2323301 - Disclosure - Subsequent Events (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SubsequentEventsTables</Role>
      <ShortName>Subsequent Events (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://roberthalf.com/role/SubsequentEvents</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2401403 - Disclosure - Summary of Significant Accounting Policies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SummaryOfSignificantAccountingPoliciesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://roberthalf.com/role/SummaryOfSignificantAccountingPoliciesTables</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/RevenueRecognitionScheduleOfRevenueDisaggregatedByLineOfBusinessDetails</Role>
      <ShortName>Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2405403 - Disclosure - Revenue Recognition - Remaining Performance Obligation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/RevenueRecognitionRemainingPerformanceObligationDetails</Role>
      <ShortName>Revenue Recognition - Remaining Performance Obligation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2405404 - Disclosure - Revenue Recognition - Schedule of Contract Liability Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/RevenueRecognitionScheduleOfContractLiabilityActivityDetails</Role>
      <ShortName>Revenue Recognition - Schedule of Contract Liability Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Other Current Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/OtherCurrentAssetsDetail</Role>
      <ShortName>Other Current Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://roberthalf.com/role/OtherCurrentAssetsTables</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2411402 - Disclosure - Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/GoodwillDetails</Role>
      <ShortName>Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://roberthalf.com/role/GoodwillTables</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Property and Equipment, Net - Components of Property and Equipment (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/PropertyAndEquipmentNetComponentsOfPropertyAndEquipmentDetail</Role>
      <ShortName>Property and Equipment, Net - Components of Property and Equipment (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - Leases - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/LeasesNarrativeDetails</Role>
      <ShortName>Leases - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - Leases - Lease Cost and Other Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/LeasesLeaseCostAndOtherInformationDetails</Role>
      <ShortName>Leases - Lease Cost and Other Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2413404 - Disclosure - Leases - Future Minimum Lease Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/LeasesFutureMinimumLeasePaymentsDetails</Role>
      <ShortName>Leases - Future Minimum Lease Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Accrued Payroll and Benefit Costs (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/AccruedPayrollAndBenefitCostsDetail</Role>
      <ShortName>Accrued Payroll and Benefit Costs (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://roberthalf.com/role/AccruedPayrollAndBenefitCostsTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2419401 - Disclosure - Commitments and Contingencies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/CommitmentsAndContingenciesAdditionalInformationDetail</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2420402 - Disclosure - Stockholders' Equity - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/StockholdersEquityAdditionalInformationDetail</Role>
      <ShortName>Stockholders' Equity - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2420403 - Disclosure - Stockholders' Equity - Number and Cost of Common Stock Shares Repurchased (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/StockholdersEquityNumberAndCostOfCommonStockSharesRepurchasedDetails</Role>
      <ShortName>Stockholders' Equity - Number and Cost of Common Stock Shares Repurchased (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2420404 - Disclosure - Stockholders' Equity - Number and Cost of Employee Stock Plan Repurchases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/StockholdersEquityNumberAndCostOfEmployeeStockPlanRepurchasesDetails</Role>
      <ShortName>Stockholders' Equity - Number and Cost of Employee Stock Plan Repurchases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2421402 - Disclosure - Net Income Per Share - Calculation of Net Income Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/NetIncomePerShareCalculationOfNetIncomePerShareDetails</Role>
      <ShortName>Net Income Per Share - Calculation of Net Income Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2422402 - Disclosure - Business Segments - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/BusinessSegmentsAdditionalInformationDetail</Role>
      <ShortName>Business Segments - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2422403 - Disclosure - Business Segments - Reconciliation of Revenue and Operating Income by Reportable Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/BusinessSegmentsReconciliationOfRevenueAndOperatingIncomeByReportableSegmentDetails</Role>
      <ShortName>Business Segments - Reconciliation of Revenue and Operating Income by Reportable Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="rhi9301910q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2423402 - Disclosure - Subsequent Events - Dividend Announced (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://roberthalf.com/role/SubsequentEventsDividendAnnouncedDetails</Role>
      <ShortName>Subsequent Events - Dividend Announced (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="rhi9301910q.htm">rhi9301910q.htm</File>
    <File>rhi-20190930.xsd</File>
    <File>rhi-20190930_cal.xml</File>
    <File>rhi-20190930_def.xml</File>
    <File>rhi-20190930_lab.xml</File>
    <File>rhi-20190930_pre.xml</File>
    <File>rhi93019ex311.htm</File>
    <File>rhi93019ex312.htm</File>
    <File>rhi93019ex321.htm</File>
    <File>rhi93019ex322.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
